1. Field of the Invention
The present invention relates to methods of wafer feature observation; in particular, to observation methods of wafer ion implantation defect.
2. Description of Related Art
In wafer fabrication, ion implantation is an essential process for changing the physical properties, and through an acceleration process, ion acquires the necessary energy to be injected into wafers and stay at a certain depth from the surface of the wafers. Since ion implantation is one of the critical factors affecting the quality of the wafer, engineers perform ion implantation analyses on flawed/defected wafers to understand whether the causes for such flaws are related with ion implantation failure, many techniques are developed for detecting implant levels, like SIMS (secondary ion mass spectrometry) and SCM (scanning capacitance microscopy), but necessary capital expenditure of these equipments are high. Another approach to visualize dopant regions is to use standard SEM (Scanning electron microscope) equipment junction staining. Before performing the analyses, it is necessary to prepare samples to be analyzed. First, engineers cleave a wafer for analysis, and perform a polishing action on these pieces of wafer with flaws. Next, immerse the sample in chemical solution in several seconds for decoration. Since the ion implantation states for P-type regions and N-type regions of the wafer are different, etching topography for P-type regions and N-type regions by the chemical decoration vary as well, such that the surface of the wafer presents a non-flat state. Finally, using scanning electron microscope to observe whether the ion implantation is successful; if the ion implantation is proven to have failed, the root cause have to be found and solved.
However, chemical decoration quite inefficient regarding the time spent on the steps of polishing and chemical decoration, which usually takes nearly one hour; and variations that may negatively affecting etching by the chemical decoration are many, for example poor control over immersion duration, or changes of properties/natures in the chemical decoration itself and the like; hence, successful operations are not easy, thereby causing low repeatability in such analysis results. Apart from this, a new method of ion implantation visualization referred as dopant contrast has been developed; however, so far its effect of use is not satisfactory due to low level of contrast.
Accordingly, the inventors of the present invention, having considered the above-mentioned improvable defects, devoting long-term efforts in researches together with field applications of theoretical knowledge, proposed the present invention with reasonable design and effective improvements over the disadvantages illustrated supra.